Add activity indicator

Riot/Modules/Common/ActivityIndicator/SwiftUI/ActivityIndicatorModifier.swift

@@ -0,0 +1,43 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+import SwiftUI
+
+/**
+ A modifier for showing the activity indcator centered over a view.
+ */
+@available(iOS 14.0, *)
+struct ActivityIndicatorModifier: ViewModifier {
+    var show: Bool
+
+    func body(content: Content) -> some View {
+        if show {
+            content
+                .overlay(ActivityIndicator(), alignment: .center)
+        } else {
+            content
+        }
+    }
+}
+
+@available(iOS 14.0, *)
+extension View {
+    @available(iOS 14.0, *)
+    func activityIndicator(show: Bool) -> some View {
+        self.modifier(ActivityIndicatorModifier(show: show))
+    }
+}